Automated computerized microdensitometric analysis of fluorescein angiograms has achieved a degree of reproducibility greater than manual methods. The initial objective will be to utilize this technique and evaluate patient and subject reproducibility over a short-term (hours) as a function of continued basal state or as a function of a meal. Following establishment of appropriate steady-state baseline conditions, mean retinal circulation time will be evaluated by this technique in four stratified groups of juvenile onset diabetics (according to duration of disease) evaluated prospectively, annually, by fluorescein angiography. In addition, every two months blood samples for determination of hemoglobin AIc, blood glucose, cholesterol, triglyceride and HDL-cholesterol will be measured. At baseline, muscle capillary basement membrane thickness will be evaluated and repeated every two years. Similar prospective studies will be performed in healthy normal controls and in genetic prediabetics (offspring of two diabetic parents and apparently unaffected monozygotic twins with a diabetic twin-mate). This population will also receive annually oral glucose tolerance tests with evaluation of serum insulin and plasma glucagon and growth hormone responses.